Electric blasting initiator



March 17, 1942.

ELECTRIC BL-ASTING INITIATOR Original Filed Dec. 24, 1937 2 Sheets-Sheet 1 c aQ M.'H. ENGLISH E 'TA| 2,276,380- I flalandflf/lfydegger Y 9 "ATroRN EY Mam}! 1942- M. H. ENGLISH EI'AL 2,

ELECTRIC BLASII'NG INITIATOR v Original Filed Dec. 24, 1937 2 Sheets-Sheet 2 9 g VENTORS k R0 azzdR gdegy ATTORNEY Patented Mar. 17, 1942 I ELECTRIC ams'rmo. mrrm'roa v Myrlc Hardt English. Pompton Lakes, N. 1., and

Roland Roswell Nydegger, Wilmington, Del., as- I signorsto E. L du Pont de Nemours a Company. Wilmington, DeL, a corporation of Dela- Original application December 24, 1931, Serial No. 181,647. Divided and this application August so, 1939, Serial No. 292,591

3 Claims.

The present invention relates to the art of forming articles from thermoplastic compositions, rubber compositions and the like, and, in particular, to an improved process for the manufacture of electric blasting initiators involving the foregoing.

This application is 'a division of co-pending application Serial No. 181,647, filed December 24, 1937, now Patent No. 2,242,117.

The introduction of thermoplastic compositions for use as insulation for electrical equipment and the like has rendered it desirable in many instances to vulcanize rubber compositions and the like in a position adjacent to or about a preformed body of a thermoplastic composition. The methods and apparatus known to the art have proven unsatisfactory-for this purpose by reason of the inherent defect, common to such methods, that the temperatures necessarily employed to initiate vulcanization and curing of the introducing said preformed body of thermoplastic material in a locus adjacent to said mold and in contact with said rubber composition therein, heating said rubber composition to a vulcanizing temperature in said mold while surrounding said body of thermoplastic-material with a cooling device causing said body to remain in a solid state. I

A useful and highly desirable adaptation of this process is the manufacture of a novel electric blasting. initiator assembly comprising a rubber composition plug vulcanized about leg wires provided with thermoplastic insulation. This adaptation of the process of our invention is carried out by introducing leg wires provided with thermoplastic insulation by way of a leg wire seal into a plug chamber in a mold, said chamber rubber composition likewise cause softening of the thermoplastic composition and subsequent intermingling of these two types of compositions. The result is undesirable from the standpoint of effective vulcanization and curing, and the strength, durability, and appearanceof the product.

The present invention has for'its object a method and apparatusfor the vulcanization of rubber compositions and the like. adjacent to a body of thermoplastic, material with the prevention of substantial intermingling of said rubber composition with said.thermoplastic composition. A further object is the adaptation of this novel method and apparatus to the production of a novel and improved electric blasting initiator assembly. Additional objects will be apparent from the more detailed description of our invention which follows.

We have found that the foregoing objects are accomplished and the disadvantages overcome by the process of our invention which comprises vulcanizing a rubber composition in juxtaposition with a preformed body of thermoplastic material substantially in the absence of the inter,- mingling of said rubber composition and said thermoplastic material by introducing said preformed body of thermoplastic material adjacent to said rubber composition, heating said rubber composition to vulcanizing temperature while conducting'heat away from said body of thermoplastic material causing said body to remain in a solid state. The foregoing process is effectively practiced by introducing the rubber composition into a mold of predetermined shape,

being supplied with a rubber composition suitable for the manufacture of bridge plugs and the like.

The mold is equipped with heating means formaintaining a vulcanizingtemperature in said plug chamber. These heating means preferablyinclude a vent in said mold adapted to the passage of the heating fluid in heat exchange relationship with said plug chamber. The leg wire seal adapted to the reception and introduction of said insulated leg wires into said mold preferably comprises a heat conducting body grooved to receive said legwires and with shape permitting its insertion into the open end of the plug chamber with substantially minimum surface engagement with said mold in order to limit heat transfer from said rubber composition and said heated mold to the thermoplastic insulation of the leg wires in said seal. The leg wire seal is provided with cooling means for the purpose of maintaining the leg wire insulation therein in a solid state regardless of the heat from said mold.

In our preferred embodiment, this cooling of the seal is accomplished by mounting the same on a' massive loading frame in heat conducting relationship with said seal to minimize temperature rise therein. With this arrangement, large quantities of heat may pass from mold to seal, but

.will immediately be conducted away from the Heat insulating means are provided between the mold and seal, reducing heat transfer.

In order to describe our invention more clearly, we shall refer to the attached drawings which 11- lustrate preferred embodiments thereof. This is done solely by way of illustration and is not to be regarded as a limitation upon the scope of our invention.

Referring generally to the figures of the drawings, Figs. 1 and 2 are views in perspective of the upper and lower sections of the grooved leg wire seal. Figs. 3 and 4 are: views in perspective oi'the upper and lower sections of the mold. Fig. 5 is a sectional view of a single leg wire seal inserted in a single plug chamber of the mold. Figs. 6 and 7 are vertical end views of the upper and lower sections of the entire mold. In Fig. '7, the leg wire seal is depicted mounted on the massive loading frame and assembled with the lower section of the mold. Fig. 8 is a view of the finished rubber composition plugmolded about the leg wires provided with thermoplastic insulation. Fig. 9 is a view in perspective of the lower section of a different embodiment showing seal and mold in combination. Fig. 10 is a view of the finished plug produced in this different embodiment of Fig. 9.

Similar characters are used wherever-possible for the several views and in the following description to designate corresponding parts.

Referring in greater detail to the drawings, Figs. 1 and 2 show the upper and lower sections of the leg wire seal I-a and I, respectively, provided with grooves 2-0 and 2, respectively, which co-operate to receivethe leg wires and hold them in place. The projections 3-a and 3 of the seal are adapted to be inserted into the open ,end of the plug chamber Ii of mold 5 of Fig. 5 formed by the co-operation of depressions 4-41 and 4 of Figs. 3 and 4, respectively. The upper and lower sections of the mold are provided with vents I-a and 1, respectively, shown in Figs. 3. 4, and 5, which vents are adapted to the passage of steam or other heating fluid in heat exchange relationship with the plug chamber 5. An enlarged view of these vents 'l-a and I is presented in Fig. 5. The leg wire seal I is preferably protected against the high temperatures of the mold by being mounted on the massive loadof the seals I. Two strips of rubber compositions are then placed on the lower section of the mold 6, following which, seals I with their supporting frame-work 8 and leg wires are engaged in the mold cavities, after which, two more strips of rubber are placed on top of the leg wires. The

said thermoplastic insulation. This result is possible because heat transferred from the hot mold to the wire seal I is immediately disseminated throughout the massive loading frame 8, which is subject to the cooling eflfect of surrounding air.

The further features of the complete, mold as shown in Figs. 6 and 7 including the double molding system based on the two rows of plugs insulation and rubber plug composition in the absence of the interminging of the two as the result of formation by the process of our invention.

A somewhat difierent embodiment is set forth in Fig. 9, which shows a different arrangement of mold and leg wire seal in combination. The leg wire seal I rests adjacent to the mold 6 at the locus of each leg wire groove 2 leading into each mold chamber 4. However, throughout the greater portion of its surface, the leg wire seal I is protected'from the heated mold 6 by the interposition of heat insulating material 9. The

leg wire seal is provided with cooling means con-' sisting of the vents I0 adapted to the passage of cooling fluid in heat exchange relationship with the leg wire grooves. The upper section of this type of mold is identical with the lower. In operating with this device, the leg wires are inserted through the grooves, chamber, and guides, rubber composition introduced into the chamber, and the mold closed. The mold is then heated by passing fluid through the vents I and simultaneously the seal is cooled by the passage of fluid through the vents III. The resulting plug is shown in Fig. 10.

The process according to our invention has the advantage that rubber compositions may be vulcanized adjacent to preformed thermoplastic bodies in the absence of the intermingling of said two types of compositions, in particular, electric blasting initiators such as, those prepared with the rubber plug, as disclosed and claimed in copending application, yet having the leg wires provided with thermoplastic insulation. By practicing the process according to our present invention, no substantial intermingling of rubber plug and thermoplastic insulation is effected which would otherwise lower the strength and water-resistance of the resulting product.

surface engagement between mold 6 and seal I is kept at a minimum, as illustrated in Fig. 5, in order to limit the heat transfer to thethermoplastic insulation supported in grooves 2 of seal I. 1's of an inch is maintained. The mold is then closed and heated by the circulation of steam through the vents '|.a and I. compressing a rubber composition plug about each set of leg wires in contact with the thermoplastic insulation thereon but in the absence of any substantial intermingling of said rubber composition with Preferably, a linear contact of not over In the foregoing we have described the preferred process and apparatus according to our invention. It will be apparent, however, that many variations may be made without departing from the scope of this invention. We intend,

however, to be limited only by the following claims.

We claim: 1. In an apparatus for molding rubber compo sition plugs on electric blasting initiator leg wires provided with thermoplastic insulation substantially in the absence of the intermingling including a vent in said mold adapted to the passage of a heating fluid i n heat exchange relationship with said chamber, with a leg wire seal including a heat conducting body grooved to receive saideleg wires and positioned in the open. end of said plug chamber, said mold and said with a, minimum surface engagement and in such manner that the chamber segments of each are inalignment, and a solid body of high con- I ductivity in heat exchange relationship with seal being joined in flxed relationship to complete the walls of said chamber with minimum surface engagement between them, and a solid body of high conductivity in heat exchange re- ;lationship with said leg wire seal.

2. In an apparatus 'for molding rubber composition plugs on electric blasting initiator leg wires provided with thermoplastic insulation substantially in the absence of the intermingling of u said rubber composition and said thermoplastic insulation, the combination of a'mold provided with a plugchamber having an open end and equipped with heating means forcmaintaining said mold being connected in fixed relationship said leg wire seal, said solid body being cooled solely by means of the atmosphere. 8. Apparatus formolding rubber composition plugs on electric'blasting initiator leg wires provided with thermoplastic insulation substantially in the absence of "the intermingling of said rubbr composition and said thermoplastic insulation, which apparatus comprises; the combination of a mold provided with a plug chamber having an open end and adapted to the reception of said rubber composition and said leg wires, and

'to the shaping of said composition about said leg wires to form a plug, and being equipped with heating means for maintaining said plug chamber at a vulcanizing temperature, with a leg wire seal including a conducting body grooved to receive said leg wires and positioned in the open end of said plug chamber, the connection between said leg wire seal and said mold representing a fixed relationship of minimum surface engagement. I

" MYRLE HARDT ENGLISH.

ROLAND R. NYDEGGER. 

